1. Field of the Invention
The present invention relates to water desalination system configurations that will provide a continuous supply of treated water without creating waste products. These systems are commonly referred to as zero waste effluent systems. A significant feature of the present designs is that they allow zero waste effluent operation without prematurely fouling the desalination membrane being used.
2. Description of the Prior Art
In the prior art it is known to purify (or treat) water through a variety of commercially available water treatment devices designed for point-of-use applications in the commercial/residential water treatment market. The most popular devices are based on the following technologies: activated carbon for organic removal; ultraviolet light disinfection; ion exchange for hardness removal (water softening), and reverse osmosis (RO) desalination.
Desalination devices that use reverse osmosis (RO) membrane elements always create two streams of water as the water exits the RO module: desalinated product water (which has passed through the membrane), and a waste brine (that has flowed across the membrane surface). This waste brine stream is necessary to flush salts and minerals away from the membrane so they don't accumulate and foul the membrane surface. A buildup of salts and minerals in the feed-water to the RO membrane must not be allowed to occur continuously or dissolved substances can precipitate and form a solid on the surface of the membrane. If this occurs, the membrane will be irreversibly scaled (fouled) and must be replaced. This characteristic of the RO membrane poses a significant problem in reducing waste effluent.
The prior art also includes descriptions of ion exchange devices used to soften so called "hard water". The problem with the prior art conventional water softening systems is they use ion exchange technology to remove the hardness components of water (calcium and magnesium ions), and exchange them for sodium ions in order to create "soft water". When regeneration of the ion exchange media takes place, a concentrated water stream of sodium, chloride, calcium and magnesium ions goes into the waste system creating an environmental waste disposal problem.
In a conventional residential or home RO water treatment system, the standard ratio of water wasted to water produced is approximately 5 to 1, or 5 gallons wasted for each gallon produced. This is true only if the product water goes to atmospheric pressure after exiting the RO module. Actually, the ratio can be as much as 10 to 1, or higher, because an air captive storage tank is commonly used to store RO product water. This form of tank exerts a back pressure that restricts water flux through an RO membrane as the tank is filling. Therefore, an appreciable amount of water is wasted with a conventional home RO system.